The present invention relates to the field of gas turbine engines and is aimed in particular at means for injecting fuel into the combustion chambers of such engines.
The combustion chamber of a gas turbine engine is functionally positioned between the compression section from which it receives the air after it has been compressed, and the turbine section that it supplies with hot gases. It is generally contained inside an annular enclosure delimited by a radially outer casing and a radially inner wall protecting the drive shafts. According to one embodiment of the prior art, the chamber in which combustion takes place is itself defined between two coaxial shell rings, one of them an inner shell ring and the other an outer shell ring, spaced apart from the abovementioned two walls by appropriate flanges or supports. The upstream chamber end, at the compressor end, is provided with an upstream cowling by means of which the incident air flow leaving the diffuser is partially distributed towards the inside of the chamber where primary combustion takes place and partly downstream of the latter, by passing it. Fuel injection means associated with air guiding deflectors form a turbulent carburetted air mixture which enters the chamber through openings formed in the end of the chamber which also comprises deflectors that control the circulation of the carburetted air.
This system does not allow for optimum combustion at all running speeds, because the conditions vary between engine idling speed and full throttle. In order to improve the operation of the combustion chamber at these various speeds and to meet requirements aimed at reducing pollution, attempts are being made at limiting, on the one hand, the formation of unburned combustion residue resulting from excessively fuel-rich mixtures and, on the other hand, the formation of oxides of nitrogen which are associated with the flame temperature.
Combustion chamber designs have been proposed that have mixers suited to idling running conditions and to full throttle running conditions respectively. For example, a dual annular combustion chamber is known, which has a radial staging of the mixers so as to form distinct combustion zones which are supplied appropriately according to the engine speed. At idle speed, only the radially outer mixers are supplied with fuel, defining primary idling combustion zones. At full throttle, the radially inner mixers are in turn supplied for optimum combustion.
Combustion chambers have also been developed which have dual annular turbulent gas flow mixers. In a mixer such as this, the fuel supplied by a central pilot injector is mixed with a first turbulent annular air flow to supply a low idle first combustion zone. The mixer comprises an additional injection device, of annular shape and coaxial with the first, delivering fuel radially onto a second turbulent air flow coaxial with the first. This second injector is supplied according to the engine demand for power. An example of this device is described in patent U.S. Pat. No. 6,484,489.
Document EP 1 531 305 describes a multipoint fuel injection device for the combustion chamber of a gas turbine engine comprising a plurality of fuel injection nozzles arranged in at least two rows, for example concentric ones, with means controlling the fuel supply separately in each of the rows. The nozzles each comprise a duct with means such as swirl inducers to create a turbulent flow therein. This device makes it possible to keep a flame, in each row of nozzles, at a temperature high enough to reduce the emissions of polluting gases.